The present invention relates to a conductive material and a method for filling a via-hole, more specifically a conductive material of high conductivity which can fill micronized via-hole without generating void, and method for filling a via-hole suitable for such the conductive material.
In electronic circuit boards and semiconductor devices, conductors are buried in via-holes formed in insulating films, for connecting interconnection layers on different levels.
As methods for filling conductors in such via-holes, conventionally method for growing conductor in a via-hole by electroplating and method for filling in a via-hole a conductive resin paste containing metal powders dispersed in an organic component have been used.
However, with the recent micronization of electronic circuit boards and semiconductor devices, diameters of via-holes are so micronized that the conventional methods for filling the via-hole are insufficient to fill such via-holes.
Specifically, in the method for filling the via-hole by electroplating, as shown in FIG. 3A, usually a plated film 106 starts to grow on the sidewall and the bottom surface of the via-hole 104. At the upper end edge, where an electric field is concentrated, and a current density is higher, a growth rate is increased in this region. Accordingly, before the inside of the via-hole 104 is completely filled with the plated film 106, the upper part of the via-hole 104 is closed, leaving a void 108 at the center of the via-hole 104 (FIG. 3B). The generation of the void 108 becomes significant as the via-hole 104 has a larger aspect ratio. Resultantly, defective conduction and resistance increases often take place, and the voids are often expanded by thermal treatment to thereby break device structures.
As an improvement of this method, a method for suppressing the growth of a plated film from the sidewall of the via-hole to fill the via-hole only by the growth of the plated film from the bottom surfaces is being studied. However, this method makes no void in the via-hole, but the plating takes much time, which results in very high costs.
The filling method using the resin paste is advantageous in costs to the filling method by the plating. However, the resin paste, which is mixtures of the organic component and the metal powders, has problems of high conduction resistances, residual gas components, low usable limit temperatures, etc.
As described above, it cannot be said that the conventional methods for filling the via-hole have been sufficient to fill micronized via-holes. A technique for filling micronized via-holes with a material of high conductivity at low costs without generating voids has been required.